That’s the call from Michael Purves, chief global strategist and head of equity derivatives research at Weeden & Co., who blasted a note to clients Wednesday saying it’s time to start shorting Tesla Motors Inc.

While acknowledging the electric-car maker has been “a nightmare of a short this year” — shares are up more than 400% — Mr. Purves expects the stock’s recent downside momentum could gain some steam in rapid fashion.

Short sellers borrow shares to sell them in hopes of buying them back at a later date, aiming to profit from price declines.

Shares recently fell more than 5% to $161. The stock has fallen 17% from the Sept. 30 record high of $194.50.

“The stock has become so divorced from fundamentals that the primary discussion needs to focus on technical analysis – which is now suggesting this year’s rally is coming to an end,” Mr. Purves says, “and that momentum is more likely exposed to the downside. While the broader tape has been bullish, this stock can drop quickly.”

Here are four “technical considerations” Mr. Purves offers as reasons investors should consider when choosing to take a short position in Tesla. From Mr. Purves:

1. Uptrend Broken. Since the stock broke decisively higher in early May, it has maintained support at the 21 day [simple-moving average] for the minor corrections and the 45 day SMA for the more significant correction (e.g. July)…Both of these supports are now broken.

2. Head and Shoulders Established. A head and shoulders pattern is developing from August with the neckline just broken. (MoneyBeat note: Head-and-shoulders is a widely-known and recognizable chart pattern. It highlights a stock’s strength in the left shoulder and the head, and the failure of the right shoulder to make a new high.)

3. Volume Higher on Down Days. As we have seen with other high momentum plays over the past few weeks, volume has been accelerating on down days. In general, volume has been picking up as the support levels discussed above have been broken.

4. Non-confirming RSI’s. Daily [relative strength indexes] have been trending steadily downwards, not confirming the higher prices reached in early October. More ominously, the weekly RSI’s have been treading steadily down from very overbought conditions and now are below 70. This pattern of non-confirming weekly RSI’s was a key sell signal for Apple when it made its life time high in September 2012.

Essentially, that means an investor could buy the Nov. $155 put, gaining the right to sell 100 shares at that price through the 15th of the month, and sell the $135 put to cut the cost. You would start to make money if the stock falls below $149.35 (the strike minus the cost).

Max profit would be $1,435 per contract.

If it falls below $155, but not below $149.35, you’d make back some of your premium, but still have a loss. Anything above $155, you lose the whole $5.65 premium ($565/contract).

Tesla is scheduled to report quarterly results Nov. 5.

–Kaitlyn Kiernan contributed to this report.

UPDATE: An earlier version of this post failed to take into account the differences in using a “put spread” as a pure short strategy versus a hedging strategy when the stock is already owned. A corrected version follows.